PDE6 inhibitor

Phosphodiesterase-6 inhibitor

Off-target: the retinal isoform of the phototransduction pathway, never the intended target
Weak PDE5-over-PDE6 selectivity is the stated basis for blue-tinged vision and light sensitivity
Sildenafil ~10-fold and vardenafil >15-fold selective; tadalafil 700-fold and avanafil >100-fold, which is why they lack the visual signature

Drugs with this mechanism (2)

Sildenafil — The first PDE5 inhibitor (Viagra); also treats pulmonary hypertension.
Vardenafil — PDE5 inhibitor for erectile dysfunction.

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